The present invention relates to a disk file apparatus for use in an information processing unit of a computer, and more particularly to an array disk system using a plurality of disk drives in which a recording surface of a disk is divided into a plurality of zones and the data capacity per track is varied in each zone to record information.
In an information processing apparatus of a computer, currently, data required by a host system, such as a central processing unit (CPU), is stored in a secondary storage system, and writing and reading of the data to the secondary storage system are carried out in response to a request of the CPU. The secondary storage system generally employs a nonvolatile storage. Representatives of the secondary storage system include a magnetic disk drive, an optical disk drive and the like.
Recently, with development of the high degree information system, high performance for the processing speed of the secondary storage system is required. As a method of improving the processing capability of a system using a magnetic disk drive, for example, there is an array disk system composed of a multiplicity of magnetic disk drives having relatively small capacity, as will be described below. The array disk system divides data transferred from a CPU and records the divided data in a plurality of magnetic disk drives simultaneously. When the recorded data is read from the magnetic disk drives, parallel processing is performed in which data recorded in each of the magnetic disk drives is read simultaneously and original data is reproduced from the data read out of the magnetic disk drives to be transferred to the CPU. In the parallel processing of the plurality of magnetic disk drives, disks constituting recording media of the magnetic disk drives are rotated in synchronism with one another in each group of magnetic disk drives which operate in parallel and the magnetic disk drives in the group are accessed using the same address. Thus, the plurality of magnetic disk drives perform the same operation.
A representative paper relating to the array disk system is "A CASE FOR REDUNDANT ARRAYS OF INEXPENSIVE DISKS (RAID)" by D. Patterson, G. Gibson and R. H. Kartz in ACM SIGMOD Conference, Chicago, Ill., June 1988. This paper reports a result of a study about performance and reliability of a one array disk system in which data of a processing unit at one time is divided and processed in parallel and an array disk system in which individual data is dispersed without dividing the data, which is treated independently. At present, the array disk system described in this paper is considered to be most popular.
In the array disk system, in order to improve the system reliability, when data is recorded, an error correction code (hereinafter abbreviated to as ECC) is generated from the divided data and the ECC is recorded in a magnetic disk drive for storing the ECC (hereinafter referred to as an ECC drive) concurrently with recording of the data. By generating the ECC as described above, when a failure occurs in one disk drive of the grouped magnetic disk drives in which the divided data is recorded and data can not be read out of the disk drive, the data recorded in the magnetic disk drive in which the failure occurs can be reconstructed on the basis of data recorded in the remaining magnetic disk drives and the ECC.
In the disk drives used in the array disk system which performs parallel processing, data is recorded in concentric tracks on the surfaces of a plurality of disks in the same manner as a conventional disk drive. Reading and writing of data in tracks on the disk surfaces are performed by reading/writing heads each provided in correspondence to a respective one of the disk surfaces, and positioning of all of the reading/writing heads to the tracks is performed simultaneously. A collection of tracks capable of being accessed by a single positioning is referred to as a cylinder and a cylinder address is commonly given to each of the cylinders from an outer periphery toward an inner periphery of the disk. Further, the capacity of data recorded in each of the tracks is the same for all of the tracks. Accordingly, in the magnetic disk drives constituting the array disk system, even if any track in any cylinder is accessed, the same capacity of data can be treated at the same time.
When parallel processing is performed in an array disk system using the type of disk drives which are commonly used at present, the physical addresses of data recorded in each of the disk drives constituting the array disk system are all identical. Thus, the disk drives are rotated in synchronism with one another and the same access instruction is issued to the disk drives, so that the reading/writing heads are caused to seek in the same direction and the same address of all of the disk drives is adapted to be always accessed simultaneously. Thus, the array disk system controls the plurality of disk drives as if a single disk drive is being used.